Time-domain correlator for spatial filtering in a pulsed energy system

ABSTRACT

A pulse compression coded type pulsed energy system having timedomain correlation means permitting narrow-band processing of wide band receiver signals without comprising the data resolution limits thereof. Local oscillator injection means provides a coded periodic sampling signal at a local oscillator input of an intermediate frequency receiver, the sampling periodicity of which sampling signal is substantially less than the system pulse repetition interval and the coding of which sampling signal is a replica of that transmitted by the pulsed energy system. The time-phase of the sampling periodicity of the sampling signal is discretely progressively varied each pulse repetition interval. Data matrix storage means responsive to the variable time-phase sampling signals reconstructs a range trace signal of improved resolution, which may be further processed by radial extent logic to effect spatial filtering within system subpulse intervals.

United States Patent l 51March 13, 1973 Vehrs, Jr.

[ TIME-DOMAIN CORRELATOR FOR SPATIAL FILTERING IN A PULSED ENERGY SYSTEM[75] Inventor: Charles L. Vehrs, Jr., Anaheim,

Calif.

[73] Assignee: North American Rockwell Corporation, El Segundo, Calif.

[22] Filed: Nov. 28, 1967 [21] Appl. No.: 686,113

[52] US. Cl ..343/17.2 PC, 343/77, 3 3/5 DP [51] Int. Cl ..G01s 9/233[58] Field of Search 343/172 PC, 171,14, 5 DP,

[ 56] References Cited UNITED STATES PATENTS 3,680,096 7/1972 Bose..343/7.7 3,680,104 7/l972 Westaway ..343/l7.2 PC

Primary Examiner-T. H. Tubbesing Attorney-William R1 Lane, L. LeeHumphries and Rolf M. Pitts [57] ABSTRACT A pulse compression coded typepulsed energy system having time-domain correlation means permitting narrow-band processing of wide band receiver signals without comprising thedata resolution limits thereof. Local oscillator injection meansprovides a coded periodic sampling signal at a local oscillator input ofan intermediate frequency receiver, the sampling periodicity of whichsampling signal is substantially less than the system pulse repetitioninterval and the coding of which sampling signal is a replica of thattransmitted by the pulsed energy system. The timephase of the samplingperiodicity of the sampling signal is discretely progressively variedeach pulse repetition interval. Data matrix storage means responsive tothe variable time-phase sampling signals reconstructs a range tracesignal of improved resolution, which may be further processed by radialextent logic to effect spatial filtering within system subpulseintervals.

27 Claims, 17 Drawing Figures I MIXER 1F VIDEO on MATRIX F sues AMPLosrscron STORAGE MEANS l l IF RECEIVER sues TR l p .i' "4 .-J

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SHEET UlUF 12 23 25 26 1 i I I MIXER 1F VIDEO 0m MATRIX sTAGE AMPLDETECTOR T" sToRAGE MEANS I I I IF RECEIVER STAGE TR L J 1E2 T h SPATIALcooeo FILTER L.O./"28 MEANS cobso v L XMTR 2 SIGNAL 1 UTILIZATION PULSEMEANS COMPRESSION coomG MEANS "2' ADJUSTABLE/29 DELAY (n-l GENERATORSHIFT REGISTER -so CLOCK J\ IL A .unumumm OUTPUT CLOCK SYSTEM TRIGGERFIG. I

INVENTOR.

CHARLES L. VEHRS JR.

ATTORNEY J I H .l

OUTPUT RECEIVED SIGNAL AMPLITUDE SAMPLED IF SIGNAL AMPLITUDE AMPLITUDEPATENTEDMAR 13 1975 3. 720.950

SHEET 02 [1F 12 Ar 2% I -1 if 3 0 I I n SYSTEM REPETITION lNTERVAL-- Fla2 INVENTOR.

CHARLES L. VEHRS JR.

ATTGR NEY PATENTEDHAR 1 31973 SHEET 03 0F 12 RECONSTRUCT ED RANGE TRACEFIG. 3

FREQUENCY (\EGACYCLES SECONDS) lcsml FIG. 6

INVENTOR.

CHARLES L. VEHRS JR.

ATTORNEY PATENTEU MAR l 3 I975 SHEET DU [1F 12 FIG.40

hvzmzammu PERIODIC TIME FIG. 5

INVENTOR. CHARLES L. VEHRS JR.

ATTORNEY PATENTEDMAR 13 1975 SHEET DSUF 12 I NVEN TOR.

LE '1" f ATTORNEY PATENTEDMAR 13 1975 sum 08 0F 12 CLOCK CLOCK CLO K IWRITE-IN ggf fl READ-OUT COMMUTATOR E STORAGE COMMUTATOR -VMATRIX mOUTPUT T0 SIGNAL- UTILIZATION MEANS I05 I96 I95 A f l I v 0 I03 'I f wSWITCH FIGIZ INVENTOR.

CHARLES L. VEHRS JR.

ATTORNEY PAIENTEU MAR \3 I975 SHEET 09 0F 12 SAMPLED VIDEO DATA CELLWRITE MODE DATA CELL STORED \NAVEFORM loo OFF

READ MODE IOI DATA CELL SWITCHED POTENTIAL VIDEO OUTPUT AMPLITUDEINVENTOR.

TlME--P CHARLES L. VEHRS JR.

FIG. I3

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ATTORNEY PATENTEDHAR 1 3 I875 3 720 950 sum 1 10F 12 "4 us ue wow Qsecono W SHIFT REGISTER ZmSQL CLOCK ill I FIRST SHIFT REGISTER I as flg.l5

us FIRST SHIFT REGISTER I: OUTPUT szcouo l 2l8 REGISTER l I I I OUTPUTGATE OUTPUT FIG. l6

INVENTOR. CHARLES L. VEHRS JR.

ATTORNEY PATENTEDMR 13 I975 SHEET 120F 12 RANGE am A 1 ACCUM/ULATOR INOR SYNTHETIC us MOVING V V V TARGET NOR VIDEO NoR 3|? sR sR SR3 sn SR2SR3 ANS $25 3|5 H6 AXES 386 VIQE A 1 INPUT 4 PRF K CIRCULATING REGISTERl2 SYSTEM J TRIGGER FIG. I?

INVENTOR. CHARLES L. VEHRS JR.

ATTORNEY TIME-DOMAIN CORRELATOR FOR SPATIAL FIIJTERING IN A PULSEDENERGY SYSTEM CROSS REFERENCES TO RELATED APPLICATIONS 1. U.S.application, Ser. No. 430,141 filed Feb. 3, 1965, by J. 0. Anderson, etal., for Radar System Having Improved Response to Small Targets, nowU.S. Pat. No. 3,500,404.

2. U.S. application, Ser. No. 476,630 filed Aug. 2, 1965, by C. R.Barrett, et al., for Multiple Frequency Radar System Having ImprovedResponse to Small Targets.

3. U.S. application, Ser. No. 488,560 filed Sept. 20, 1965, by D. C.Coleman, et al., for Fully Coherent Multiple Frequency Radar System.

4. U.S. application, Ser. No. 593,237 filed Nov. 7, 1966, by G. P.Cooper for A Wideband Pulsed Energy System.

5. U.S. application, Ser. No. 639,238 filed May 7, 1967, by J. A.Moulton for Range-Gated Moving Target Signal Processor.

BACKGROUND OF THE INVENTION In the tactical use of pulsed energysystems, such as airborne military radars, the targets of principalinterest are generally sharply defined objects such as armored tanks,trucks, bridges or buildings which are small relative to surroundingterrain features, and relative to the range resolution and angularresolution of the system. Such small targets are difficult todistinguish amid the clutter return from the terrain (or rain) or fromlike targets of large radial extent relative to the range resolution ofthe radar system pulsewidth and lying at a similar range and directionas the small target of tactical interest.

In the case of a small moving target, fast moving radially relative tothe clutter-producing background, the spectral content of the smalltarget echo may be distinguished from the spectral content of the smalllarger clutter return by means of the relative doppler shift betweenthem by prior art AMTI techniques, as is well understood. However, wherethe velocity of the tactical target relative to the clutter-producingbackground is very low (as in the case of slow moving military groundvehicles or stationary tactical targets) or the bandwidth of the clutterspectrum is very wide (due to a large antenna beamwidth or largelook-angle), the lesser spectral content of the tactical target radarreturn may lie within the spectrum of the larger clutter return, wherebythe doppler filtering of AMTI techniques cannot be effectively employed.

Attempts to enhance the detection of a small target echo contained inclutter return have included timecoherent integration or the additivecombining of corresponding range portions of the range trace signalsreceived during a selected member of successive pulse repetitionintervals by means of a tapped delay line or scan converter, asdescribed for example in U.S. Pat. No. 3,113,311 issued Dec. 3, 1963, toSearle and Henderson for a Radar Integrating System. However, suchtechnique is of limited effectiveness clue to the amount of signalstorage capacity required, and the allowable length of the dataprocessing interval limits the obtainable minimum signal-to-clutterratio. In other words, the minimum clutter content is yet limited by thetransmitted pulsewidth employed by the pulsed energy system.

Although the use of a narrow transmitted pulsewidth obviously serves toimprove range resolution and signal-to-clutter ratio, such techniqueimposes rangeperformance limitations upon a peakpower limitedtransmitter. Other means sought for improving the range resolution orsignal-to-clutter ratio have employed pulsecompression techniques inwhich a transmitted pulse is selectively modulated, and the receiver(filter) responds to compress a received echo of the modulated pulseinto a much shorter one. A description of such pulse compressiontechniques, including frequency-modulation pulse compression andphasecoded pulse compression is included in Section 10.9 of Introductionto Radar Systems by Skolnik, published by McGraw-Hill (1962). A basicshortcoming of such technique is the difficulty in reducing theprinciple to practice, due to the frequency stability requirements andthe difficulty of matching the receiver-filter to the transmittermodulation. Also, the theoretical resolution limit or pulse compressioneffect of such techniques normally requires a higher bandwidth than thatconveniently obtainable in the compression filter, intermediatefrequency and video stagesof the receiver. In other words, receiverbandwidth limitations compromise the theoretical high resolution limitsand determine the actual resolution obtained from classical pulsecompression techniques.

Discrete multiple frequency techniques (such as those described incopending U.S. application, Ser. No. 430,141 filed Feb. 1965, U.S.application, Ser. No. 476,630 filed Aug. 2, 1965, and U.S. application,Ser. No. 488,560 filed Sept. 20, 1965, all of which applications areowned by North American Rockwell Corporation, assignee of the subjectinvention) have been utilized to improve signal-to-clutter ratio, butemploy an undesirably large transmitted bandwidth. Such disadvantage issought to be avoided by combining the chirp-transmission of a frequencymodulated pulse compression type system with the further coding andreceiver processing of the multiple frequency technique, as taught inU.S. application, Ser. No. 593,237, owned by North American RockwellCorporation. However, all of such multiple frequency and pulsecompression techniques yet suffer from signal-tonoise limitationsassociated with such widebandwidth processes. Also, the display circuitsof such systems require high threshold levels in order to avoidresponding to random fluctuations in large clutter returns. In otherwords, in order to discriminate between a source of clutter and adiscrete target, the target signal amplitude must be significantlylarger than the average amplitude of the clutter return.

In an article, Pulse Compression Research in the United Kingdom" by E.H. Boyenval and comprising Chapter 4 of the text Radar Techniques forDetection, Tracking and Navigation," edited by W. T. Blackband andpublished by Gordon and Breach Science Publishers (1966), there isdescribed a time correlator technique for effecting pulse compression bythe use of a single local oscillator waveform input to a tapped delayline, the local oscillator waveform being similarly chirped as atransmitted waveform. Correlation of the discretely delayed localoscillator samples with the received RF echoes produces IF signals, theIF frequency components of each of which correspond to a discrete rangeor separate range bin. A sampling gate at the output of each IF filtergates out the response of such filter for a sampling intervalcorresponding to the pulsewidth and occurrence of the associated localoscillator input in response to a gate control or sampling pulse inputhaving a like duration as the delayed local oscillator waveform and aperiodic occurrence corresponding to the delay of such local oscillatorwaveform.

In reconstructing a range trace signal of improved resolution by meansof the mechanization disclosed by Boyenval, it is necessary to employ atleast one IF filter per tap of the tapped delay line, no provision beingmade for time sharing of a single filter of a given bandwidth by allsampled intervals. Such large minimum number of IF filters, utilized bysuch tapped delay line mechanization, is made further necessary in viewof the gating interval employed by the IF filter output gating means.Further, although the combined IF output of the gated filters representsa range trace signal of reduced overall clutter content, no processingis taught for distinguishing discrete clutter elements thereof fromcultured targets of interest. Moreover, the use of a delay line limitsthe obtainable resolution (or compromises resolution performance) due todelay line bandwidth limitations.

SUMMARY OF THE INVENTION By means of the concept of the subjectinvention, a coded wide bandwidth pulse transmitter cooperates with aninherently gated narrow bandwidth intermediate frequency receiver toprovide a sampled range trace signal having an inherent resolutioncorresponding to the reciprocal of the transmitted bandwidth, and havingan improved signal-to-noise ratio.

In a preferred embodiment of the invention, there is provided atime-domain correlator, including local oscillator injection means incooperation with the intermediate frequency receiver for injecting acoded periodic sampling signal at a local oscillator input of theintermediate frequency receiver, the sampling periodicity of thesampling signal being substantially less than the pulse repetitioninterval of the pulsed energy system, and the coding of which codedsampling signal is a replica of that transmitted by the pulsed energysystem and representing a bandwidth the reciprocal of which is less thanthe sampling period, whereby a sampled range-trace signal of improvedresolution is provided. The time-phase of the sampling periodicity isdiscretely progressively varied each pulse repetition interval by anamount less than the'coding bandwidth. Data matrix storage meansresponsive to the variable time-phase sampled receiver signalsreconstructs a range trace signal having an improved range resolutionand reduced clutter content.

By means of the above-described arrangement, normally narrow bandwidthreceiver (intermediate frequency and video) circuits may be employed toeffect high resolution processing (high signal-to-clutter ratio) whileretaining high signal-to-noise ratios. Also, because of the highresolution limits thus obtained, sophisticated logic may be employed tospatially filter such data, including automatic thresholding of eachrange bin (e.g., range-bin thresholding) and avoiding the false targetindications resultingfrom prior-art average-thresholding over therange-trace. Moreover, such logic may further include means fordistinguishing such thresholded targets on the basis of radial extentdiscrimination and radial velocity discrimination (rate of change orrange). Accordingly, an object of the invention is to provide animproved time-domain correlator for a pulsed energy system.

Another object of the invention is to provide a pulsed energy systemcorrelator providing both improved signal-to-clutter ratios andsignalto-noise ratios.

Still another object'of the invention is to provide time-domaincorrelator means allowing narrow bandwidth receiver processing of widehand signals in a pulsed energy system.

A further object is to provide a pulsed energy system having asubstantial range resolution improvement over that range resolutionrepresented by the transmitted pulsewidth.

Yet a further object is to provide narrow bandwidth means forcooperation with a wideband pulsed energy system for spatial filteringof range trace signals received by said system.

Still another object of the invention is to provide processing ofwideband system pulse compression signals for target qualification as tothreshold, amplitude, and radial extent.

These and further objects of the invention will become apparent from thefollowing description, taken together with the accompanying drawings, inwhich BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified blockdiagram of a system embodying the concept of the invention;

FIG. 2 is a representative family of the histories of the response ofthe system of FIG. 1;

FIG. 3 is an alternate representation of the sampled range trace signalsof FIG. 2, illustrating the manner of effecting a reconstructed rangetrace signal of improved resolution by means of the data matrix storagemeans of FIG. 1.

FIG. 4 is a family of representative time histories of the correlatorconcept of FIG. 1, for a frequencymodulation coding.

FIG. 5 is a composite periodic time history of the response of thedevice of FIG. 1 for a frequency modulation coding.

FIG. 6 is a spectral diagram of the input to the IF amplifier of FIG. 1relative to the bandwidth of such amplifier, showing the effects ofmatching the bandwidth to the injected pulsewidth,

FIG. 7 is a block diagram of a frequency modulated pulse compressionsystem embodying another aspect of the invention;

FIG. 8 is a schematic arrangement of range-bin thresholding data matrixmeans in cooperation with a radial extent spatial filter;

FIG. 9 is a block diagram of a two-limit amplitude comparator, employingthe thresholding means of FIG. 7; and

FIG. 10 is a block diagram of a processor for a pulse compressionreceiver for qualifying a target as to amplitude, radial extent andradial rate;

FIG. 11 is a block diagram of a peak detecting data cell storage matrixfor processing high-resolution range video signals;

FIG. 12 is a schematic arrangement of a peak-detecting signal storageelement of the data cell storage matrix of FIG. 11;

FIG. 13 is a family of time histories illustrating an exemplary mode ofresponse of the device of FIG. 12;

FIG. 14 is a block diagram of a schematic arrangement forfurther'qualifying a high resolution moving target signal as to targetvelocity;

FIG. 15 is a block diagram of an alternate arrangement for velocitydiscrimination of moving targets;

FIG. 16 is a family of representative time histories of the response ofthe device'of FIG. 15; and

FIG. 17 is a preferred embodiment of the conceptual arrangement of FIG.15.

In the figures, like reference characters refer to like parts.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, thereis illustrated a simplified block diagram of a system embodying theconcept of the invention. There is provided a coded pulsed energysystem, comprising a pulsed radar transmitter 20 responsive to periodiccoding means 21 for providing a preselectively coded pulsed transmissionat a preselected system pulse repetition interval (provided by a systemtrigger). There is also provided a narrow band intermediate frequencyreceiver stage 22 comprising a mixer stage 23 having a local oscillatorinput 24, an intermediate frequency amplifier 25 and a video detector26, cooperatively arranged in a manner wellunderstood in the art. Codingmeans 21 cooperates to provide a series, or pulse train, of codedoutputs the periodicity of which correspond substantially to the pulsewidth of the pulsed energy transmitted by transmitter 20, for reasonswhich will become more fully apparent hereinafter. However, transmitter20 is triggered at pulse repetition intervals which are, of course,substantially greater than either the periodicity of coding means 21 orthe pulsewidth of the pulsed energy transmitted by transmitter 20.

There is further provided, in FIG. 1, time domain correlation meanscomprising local oscillator injection means in cooperation with theintermediate frequency receiver 22 for applying a coded periodicsampling signal at the local oscillator input 24 of intermediatefrequency receiver 22, the sampling periodicity of which coded samplingsignal is substantially less than the pulse repetition interval of thepulsed energy system and the time phase of which sampling periodicity isdiscretely progressively varied each pulse repetition interval by anamount less than the sampling periodicity. The coding of the codedsampling signal (on line 24) is a replica of that transmitted by codedtransmitter 20. Such coded local oscillator injection means in FIG. 1 iscomprised of a coded local oscillator 28 responsively coupled to codingmeans 21 for periodically providing a local oscillator output signal,coded similarly as the coded system transmission. Coding means 21, inturn, is coupledto a periodic impulse source or clock by avoltage-controlled delay generator 29. The time-phase of the periodicityof the coded local oscillator output is discretely adjusted, orprogressively varied, each pulse repetition interval relative to thesystem trigger by control means such as a shift register 30 responsivelycoupled to the system trigger for applying weighted, or digitally coded,control signals to a control input of delay generator 29.

The cooperation of transmitter 20, receiver 22 and coded localoscillator 28 may be more easily appreciated by reference to FIG. 2.

Referring to FIG. 2, there is provided a family of representative timehistories of the response of the system of FIG. 1. Curve 36 representsthe amplitude envelope output of transmitter 20 in response to thecombined input from the system trigger and coding means 21;'curve 37represents the amplitude envelope output of local oscillator 28 inresponse to the input from coding means 21, illustrating a periodicitysubstantially less than the pulse repetition interval of curve 36 andhaving a time phase relation (t,,) thereto which is progressivelyincreased each succeeding system pulse repetition interval. Curve 38represents the time delay or change in time phase relation of curve 37to curve 36 imparted by the cooperation of elements 29 and 30 in FIG. 1,and shows the progressive increase in discrete value each pulserepetition interval. Curve 39 represents the amplitude envelope of arange trace echo signal received in response to transmitted energypulse; while curve 40 represents the sampled intermediate frequencysignal output amplitude of mixer 23 in response to the cooperation ofmixer 23 and local oscillator 28, and corresponds to the modulation ofcurve 39 by curve 37. In other words, mixer 23 (in FIG. 1) provides anintermediate signal output in response to the application of a receiversignal only during the injection of a local oscillator signal on inputline 24, which reduces the RF receiver signal to an intermediatefrequency. Thus, local oscillator 28 (in FIG. 1) cooperates with mixer23 to gate IF receiver stage 22, whereby a sampled, or lumpy," IF rangetrace signal is provided. The duration of each signal sampling intervalAr corresponds to the transmitted pulsewidth due to the cooperation ofthe replica coding of local oscillator 28 (e.g., coded similarly as thetransmitted pulse)and the narrow bandwidth of IF amplifier 25. However,the target resolution represented by each lumpy" sample of the sampledrange trace signal corresponds to the reciprocal of the transmittedbandwidth.

In other words, only the coded echo from that range corresponding to therange time of an interval sampled by local oscillator 28 will result inan intermediate frequency signal which will, during all of such specificinterval, result in an intermediate frequency signal output having acomponent lying within the bandpass of narrow band IF amplifier 25.Other signal returns from greater or lesser ranges will not so cooperatewith such specific local oscillator sampling injection, and theresultant broadband IF components will not appear at the output offilter-amplifier 25. Where the reciprocal of the coded transmitterbandwidth is less than the receiver sampling, or gating, intervalemployed, then the resolution provided by such sampling intervalrepresents that lesser interval or finer resolution of the transmittedbandwidth; and the output energy of IF amplifier 25 over the largerperiod of the sampling interval represents the time-integration of thetarget return for a discrete target at such sampled range (e.g., locatedwithin such gated range bin).

Accordingly, it is appreciated that during each system pulse repetitioninterval narrow band IF receiver stage 22 and coded local oscillator 28cooperate with coded transmitter to provide a sampled range trace signalhaving a resolution representing the reciprocal of the broad bandwidthof the transmitted RF signal. By progressively changing the timephase ofthe coding of local oscillator 28 relative to the system trigger eachpulse repetition interval, enough narrow band IF range samples mayultimately be obtained from which to reconstruct a complete range tracesignal. For example, by progressively adjusting the time delay ofgenerator 29 each pulse repetition interval by an amount t correspondingto the reciprocal of the transmitted RF bandwidth (l/BW a sampling ofthe successive range bins of a complete range trace may be completed bythe single IF amplifier (of FIG. 1) in n pulse repetition intervals:

" 2 (BWRF)/(BWIF) where: BW intermediate frequency bandwidth of each IFfilter-amplifier In other words, signal processing speed is traded-offagainst, or compromised in favor of, reduced bandwidth in the signalprocessor and reduced number of IF filters without, however,compromising signal-toclutter performance and signal-to-noiseperformance.

Such series of variable time-phase sampled signals may be video detectedby detector 26 (in FIG. 1), to provide video signals (curve 41 in FIG.2) suitable for storage in data matrix storage means 31 (in FIG. 1) forreconstructing a range trace signal having an improved range resolution,as shown more particularly in FIG. 3.

In a specific arrangement, the coding provided by coding means 21 (ofFIG. 1) may be of the chirp or frequency-modulation type, as shown moreparticularly in FIGS. 4 and 5.

Referring to FIG. 4, there is illustrated a family of time histories ofthe response of that arrangement of FIG. 1 for which frequencymodulation may be employed as the coding technique. Such time histories,shown in an exaggerated and compressed time scale for convenience inexposition, include curves 36 and 39 representing the respectiveamplitudes of a transmitted pulsewidth and a received echo from adiscrete target (at range R,) while curves 70, 71 and 72 represent therespective frequency variation with time of the chirped transmittedpulsewidth, the received echo from a discrete target (at range R and alocal oscillator injection pulse (injected at range time t correspondingto the occurrence of that target signal represented by curves 37 and71).

It is to be seen from a comparison of curves 71 and 72 in FIG. 4 thatwhere a preselected difference frequency (f is maintained between thetransmitted frequency waveform (as reflected by the received echo signal71) and the local oscillator injection (curve 72), such preselectedfrequency may be observed between the received echo and the localoscillator during the interval of the local oscillator injection, whensuch injection occurs in time phase with the received echo. In suchcase, such difference frequency is manifested at the output of mixer 23(in FIG. 1) as an input within the bandpass of IF amplifier 25, and isfed to detector 26 for envelope detection thereof. Where, however, in asubsequent, system pulse repetition interval the timephase of the localoscillator injection is discretely varied (relative to range time asshown by the relation of curve 172 to curve 171 in FIG. 4, then a largerdifference frequency, f occurs at the output of mixer stage 23 (of FIG.1), which larger IF frequency is outside the pass band of IF amplifier25. Hence, a given time phase-adjusted local oscillator injectionresults in sampling a given subpulse interval of a range-trace duringthat system pulse repetition interval associated with such time-phaseadjustment. In other words, the frequency-scanned local oscillator isoperated repetitively within each system pulse repetition interval forsampling portions of a range trace signal, the timephase of thefrequency-scanned local oscillator pulse train being discretely,progressively adjusted each successive system pulse repetition interval,as shown in FIG. 40. The effect of such progressive adjustment of thelocal oscillator injection, in providing a sampled range trace, is shownfor the periodic time interval of a range trace in FIG. 5 for n pulserepetition intervals (PRI PRI Although the processing time toreconstruct a range trace signal of improved resolution for the singleIF filter-amplifier 25 of FIG. 1 has been indicated as n/PRF, where n isequal to the ratio of the RF bandwidth to the IF amplifier bandwidth,such processing interval may be reduced by the use of parallel channelsor IF filters, each successive one having a center frequency greaterthan the preceding one by an amount equal to at least the IF bandwidthand the incremental delay employed by delay generator 29 correspondinglyincreased (and the number of delay increments reduced).

Referring to FIG. 7 there is illustrated in block diagram a preferredembodiment of one aspect of the invention, employing frequencymodulation coding. There is provided pulse compression coding meanscomprising a narrow pulse generator 46 drivingly coupled to dispersivedelay means 47 by a first RF switch 48 during a transmit mode, toproduce a frequencymodulated RF pulse, substantially in accordance withthe teaching of the above-noted U. S. application Ser. No. 593,237 filedby G. P. Cooper. Such frequencymodulated RF pulse output of delayelement 47 is coupled to an RF power amplifier 49 by a second RF switch50 during the transmit mode.

In the receive mode of switches 48 and 50, receiver signals from theoutput of a receiver RF amplifier 51 are fed through dispersive delayline 47 to an input of an image frequency rejection type mixer 52 forconversion to an intermediate frequency, which intermediate frequency isfiltered by an IF amplifier 25 prior to envelope detection by videodetector 26. Pulse compression is effected by the cooperation of theswitched dispersive delay element 47 in such arrangement with STALOfrequency coding means.

Such STALO means comprises a stable local oscillator (STALO) 53, theoutput of which is frequency-doubled by a first frequency multiplier 54,mixed with the output of pulse generator 46 by a mixer 55, and thenbandpass limited by a filter 56 for providing a spectral outputfcorresponding to the sum or upper sideband of the pulse generatoroutput spectrum and the doubled STALO frequency, which spectral outputis chirped by delay element 47 for pulsed transmission.

Receiver RF signals, including received echoes of the chirped, pulsedtransmission, are mixed at a first receiver-mixer 57 with a second STALOsignal having a frequency (4f,) double that of the STALO input to mixer55. In this way, an upper and lower sideband signal are created:

The first term in the right-hand member of Equation (1) represents thelower sideband component of the output of receiver-mixer 57 andcorresponds to the conjugate sideband of that transmit-mode output ofdelay element 47 transmitted in response to the gated input theretoapplied from filter 56. In other words, by bandpass filtering only suchlower sideband component by a bandpass filter 58, a frequency-modulatedreceiver RF signal is provided which is oppositely modulated relative tothe frequency-modulated transmitted RF signal. Accordingly, theapplication of such lower sideband receiver signal at terminal 60 ofdispersive delay 47 by switch 50 (during the receiver mode or portion ofa pulse repetition interval) will produce an oppositely dispersiveeffect from that provided by applying the upper sideband output offilter 56 at terminal 59 (during the transmit mode). Hence, pulsecompression (f,,') of the spectrum f will result in the application ofthe lower sideband output of filter 58 to terminal 60 of delay element47, the compressed pulse output appearing on terminal 59 of delayelement 47. In other words, f =f 1 Because the same delay line elementis used for compression as is used for transmitter chirp coding, noproblems arise in the matching of the pulse compression function to thechirp function as in prior art pulse compression systems, and the actualpulse compression effect obtained by the arrangement of FIG. 4 morenearly approaches the theoretical limit defined by the reciprocal of thetransmitted RF bandwidth.

The pulse-compressed RF receiver output on terminal 59 (of dispersiveline 47) is fed by switch 48 to image frequency rejection mixer 52 whichcooperates with the injected periodic output of filter 56 to reduce suchcompressed RF pulse to an intermediate frequency. Such reduction orfrequency translation is accomplished by two successive mixing stages.The first mixer stage comprises a mixer 62 coupled to the receive" or Rterminal of RF switch 48 and having a reference input coupled to aperiodic source of the frequency [f (f, +f,,-)]. Such source, in turn,includes a mixer 64 input-coupled to STALO 53 and an intermediatefrequency (f,,-) oscillator 63 and output-coupled to a bandpass filter65, responsive to the upper side band (f, f,,-) of the output of mixer64. Such output is combined with the periodically pulsed output (f offilter 56 by a mixer 66, the output of which is bandpasslimited by afilter 67 to the lower sideband thereof U,- (f, +f, This latter signalis employed as a local oscillator input to mixer 62, which provides anupper and lower sideband output: f1 ifr (f|+flr)] (fi+flr)+[fr"(fl+flr)l The first expression (f, "'f;) of the right hand member ofEquation (2), corresponding to the lower sideband of the output ofmixture 62, is bandpass filtered by an RF filter 68 at the output ofmixer 62 and applied to another mixer 69. Mixer 69 employs the output (fof STALO 53 as a local oscillator input to reduce the output of filter68 to a lower sideband component which is bandpass filtered by IFamplifier 25:

f.- (fn' 'fm) =f1r (3) Such IF signal, occurring within the bandpass ofIF amplifier 25, occurs in the time domain only for a pulse compressionreceiver input to mixer 62 (of mixer means 52) which is coincident withthe occurrence of the injection of the coded pulse output of filter 56into mixer 66 (of mixer means 52). By operating narrow pulse generator46 repetitively within a transmitter pulse repetition interval inresponse to a system clock input, a sampled range trace interval isprovided by the output of IF amplifier 25. By adjusting the time phaseof the clock input to pulse generator 46 each transmitter pulserepetition interval, by means of adjustable delay generator 29, anentire range trace signal may be reconstructed by suitable data matrixstorage means, as indicated in connection with the description of FIGS.1 and 3. In other words, pulse generator 46 is pulsed at the beginningor transmit mode of a transmitter pulse repetition interval, in responseto the system trigger, in synchronism with the operation of RF switches48 and 50 in the transmit mode; and is then repetitively pulsed duringthe remainder or receive portion of the system trigger pulse repetitioninterval in response to a selectively delayed clock input, the delaybeing progressively varied by a discrete amount each system triggerpulse repetition interval.

Alternatively, a commercially available single-sideband mixer channelcould be employed rather than the image rejection mixer stage 52 of FIG.7. However, such single sideband devices suffer from the disadvantage ofproviding only limited sideband rejection due to phase alignmentproblems.

Accordingly, it is to be appreciated that the arrangement of FIG. 7represents a frequency modulated pulse compression system including anintermediate frequency receiver stage 22 having a receiver-mixer 69,STALO 53 and IF amplifier 25, and further including a source 56 of aspectrum to be transmitted (f Elements 64, 65, 66 and 67 comprisefiltered mixing means responsive to sources of frequency ff, and f forproviding a local oscillator injection signal spectrum (f (f, +f,Elements 62 and 68 comprise first receiver mixing means responsive to apulse compressed receiver output (on line 70) and having a localoscillator input 71 responsive to the local oscillator injection signalf,--- (f, +f p)) for providing a lower sideband frequency translatedoutput (f, +f to an input of the receiver-mixer 69 of the intermediatefrequency receiver stage 22. Elements 47, 48 and 50 comprise switchabledispersive delay means having transmit and receive modes, such delaymeans input-coupling source 56 of coding spectrum f, to a transmitter 49during the transmit switching mode to provide frequency modulation of apulsed transmission. Elements 57 and 58 comprise radio frequencyconditioning means in cooperation with STALO S3 for converting receivedechoes of the transmitted radio frequency spectrum to a lower sideband(21" 1",) of the combination of the coding spectrum (f and twice thefrequency of STALO 53. Switchable delay means 47, 48 and 50, during thereceive switching mode thereof, are interposed in circuit between anoutput of radio frequency conditioning means 57, 58 and an input offirst receiver mixing means 62 for providing (on line 70) a pulsecompressed RF receiver input of mixer 62 of IF stage 52.

Hence, it is to be appreciated that a pulse compressed IF input isprovided to the video detectors 26 of FIGS. 1 and 7 by means of'narrowbandpass IF filter means 25. For example, for a transmitted pulsewidthof 0.10 microsecond (corresponding to the reciprocal of an IF bandwidth(BW of 20 mc for IF receiver amplifier 25 (see FIG. 6), and having afrequency-modulation bandwidth (BW of 1,000 me, the pulse-compressioneffect obtained corresponds to the reciprocal of the RF bandwidth andrepresents a range resolution ofless than 1 foot.

In other words, by matching the system pulsewidth and IF bandwidth, thesystem range resolution varies inversely with the RF bandwidth and issubstantially unaffected by the actual system pulsewidth employed.

Such high resolution data, obtained by means of ordinary low-bandwidthIF receiver processing, may require further processing in order toobtain useful information or, more particularly, to distinguish andextract the additional information obtainable from such high resolutiondata. Such additional processing may include processing by data matrixmeans for reconstructing a range trace signal of improved resolution, asshown in FIG. 8.

Referring to FIG. 8, there is illustrated signal processing means forreconstructing a range trace signal from the sampled data provided bythe correlator arrangements of FIGS. 1 and 7. Such means include atapped delay line 73 having a plurality of taps responsively connectedto an input terminal 74 which is coupled to the output of video detector26 (of either FIG. 1 or FIG. 7). The interval between adjacent ones ofsuccessive taps corresponds to the system pulse repetition interval(e.g., reciprocal of the pulse repetition frequency, PRF), the number ofsuccessive taps corresponding to the number (n) of pulse repetitionintervals required to effect range trace sampling. By means of sucharrangement, the sampled data of such (n) pulse repetition intervals fora discrete progressive time phase interval associated with eachsuccessive pulse repetition interval, are combined at terminal 75 toprovide a composite or reconstructed range trace signal of improvedresolution, corresponding to that illustrated in FIG. 3.

Although the clutter content tends to be reduced by the above-describedpulse compression and timedomain correlation techniques, yet it may bedesired to threshold the receiver signals in order to more readilydiscern a discrete target amid a clutter background. For this reason, itmay be desirable to include means for separately establishing thethreshold within each sampled range bin, as a function of the signalconditions therein. Such automatic range-bin signal thresholding meansis shown in FIG. 8 as comprising a plurality (n) of thresholding means76, each interposed between a respective tap of tapped delay line 73 andinput terminal 74 for separately thresholding each of the range bins ofa range-bin set sampled in a cordelay.

responding pulse repetition interval. Such threshold (for a given rangebin) is developed as a function of the time-averaged amplitude of thesignal return for a given range-bin.

For example, for a first sampled range bin set R R R signal averages areobtained and stored by a plurality of mutually parallel switchedintegrating means C C C each of which is switched across the unipolarvideo input provided by terminal 74 during a respective samplinginterval associated with range time t 2 Each of such range-gatedtimeaveraged signals are compared with the corresponding range-bin orportion of a current range-trace signal by comparator means, which maycomprise a differential amplifier 77 and blocking diode 78, forproviding an output only for that much of a range-bin signal amplitudein excess of the time-averaged amplitude associated with such range bin.Where desired, impedance isolation amplifiers 79a and 79b may beinterposed between terminal 74 and the two inputs of an automatic rangebin signal thresholding network. The switching of the switchedcapacitors C C C may be effected by field-effect transistors or the likeresponsively coupled to the system trigger or a system clock by delaymeans such as a shift register or tapped delay line, the time intervalbetween adjacent ones of successive switches corresponding to thetime-domain correlator sampling interval employed within the sampledpulse repetition interval.

For a second or subsequent sampled pulse repetition interval, 2/(PRF)n/(PRF), the sequential switching of the range-gated time-averagingmeans 85, or switched capacitors, of a second signal thresholding means76 is delayed by the associated time-phase amount of the correlatorlocal oscillator injection delay and accomplished during that systempulse repetition interval associated with such local oscillatorinjection Such system pulse repetition interval synchronization of eachrange-gated time averaging means may be achieved by employing the sameshift register 30 as is employed by the adjustable delay generator 29(of FIG. 1) or by a suitable output from the system clock of FIG. 7, orlike counting means well understood in the art.

If, desired, the effective threshold provided by the range-bin signalthresholding means of FIG. 8 may be adjusted by adjusting the relativegain of the rangegated time-averaged signal input to the comparatoramplifier 77 (relative to the second input thereto) by means of apotentiometer or the like (not shown).

The thresholded range trace signal output on terminal of signalcombining means 73 may be further processed to distinguish thresholdedfluctuations in clutter (having a large radial extent) from a discretetarget of interest. Such processing is provided in FIG. 8 by limitspatial filtering means for indicating the detection of a target havinga radial extent within preselected minimum and maximum radial extentlimits. Such filtering means comprises first and second coincident logicsignalling means 80 and 81, and a first and second tapped delay linemeans 82 and 83, (shown as shift registers), each having an inputcoupled to terminal 75 as an input terminal, and further having aplurality of successive taps, the interval between adjacent tapscorresponding to a sampled range-bin. The plurality of taps of firstdelay line 81 corresponds to a preselected minimum radial extent, and isinput coupled to logic gate 80; the taps of second delay line 83, whichincludes a like plurality as element 82 and corresponding to apreselected maximum radial extent, are input-coupled to gate 81.Although such tapped delay line means has been shown as comprising shiftregisters, scan converters or core memory means could be employed,alternatively.

There is also provided a third coincident logic gate 84 responsive to acoincident input state of gate 80 and a non-coincident state of gate 81for providing an output signal. The simultaneous occurrence of a signalfrom each of the inputs to gate 80 indicates a thresholded signalcorresponding ma target having'a radial extent corresponding to at leastthe minimum number of contiguous range bins represented by suchplurality of inputs. The absence of a simultaneous occurrence of asignal from all of the inputs to gate 81 indicates the absence of atarget having a radial extent corresponding to at least the number ofcontiguous range bins represented by such plurality of inputs.Accordingly, an output signal from gate 84 in response to the coincidentinput state of gate 80 and non-coincident input state of gate 81 isindicative of a thresholded target having a radial extent within thepreselected upper and lower radial extent limits.

Although the spatial filter arrangement of FIG. 8 has been described interms of two delay line elements 82 and 83, it is clear that only oneelement 83 need be employed, with the plurality of taps thereof employedby gate 81 including those taps employed by gate 80.

Although range-bin thresholding and two-limit radial extentdiscrimination may be employed to distinguish a discrete target from aclutter background in the utilization of pulse-compression system data,further discrimination may be desired, where the amplitude of theclutter background varies considerably, relative to both thetime-averaged threshold and the component energy of the discrete targetreturn, such as in the case of a clutter source formed by the ocean'ssurface. In such event, it may be desired to include upper limitamplitude discrimination with the thresholding function, to avoid afalse target alarm" due, for example, to a momentary high clutter returnas shown in FIG. 9.

Referring to FIG. 9, there is illustrated a two-limit range-gatedamplitude discriminator employing the range-gated time-averaging means85 of FIG. 8 and a lower limit comparator 86, corresponding to elements77 and 78 of FIG. 8. There is also provided an upper limit comparator 87having the reference input from time-averaging means 85 selectivelybiased to provide an upper limit, and arranged to provide an output whenthe amplitude of the range trace signal on terminal 74 does not exceedsuch upper limit. A signal gate 88 responsive to comparators 86 and 87provides an output signal during the interval that the input on terminal74 exceeds the lower limit input to comparator, while not exceeding theupper limit input to comparator 87.

Such a two-limit amplitude comparator may be em ployed in thearrangement of FIG. 8, alternative to each of the automatic range'binsignal thresholding means 76, whereby a qualified target signal isprovided, being qualified as to two-limit amplitude discrimination andtwo-limit extent discrimination.

Often it may be desired to effect range-rate (radial rate)discrimination among the plurality of qualified target return signalsobtainable from a pulse compression system. The use of doppler filteringtechniques in prior art pulsed energy AMTI systems relies on the use ofa system range resolution large enough, relative to the target size andspeed, to allow observation of the target within such range bin overmany pulse repetition intervals, whereby the doppler shift phenomenonmay be discerned. Although doppler filtering has been employed for AMTIpurposes in prior-art systems, such technique may be of limitedeffectiveness in a pulse compression system, in view of the high rangeresolution or small range-bin samples represented by the data elementsutilized. In other words, a moving target will normally not remain in agiven one of the small range bins (of a pulsed compression system) longenough to allow the observation of the doppler phenomenon. Also, becauseof the reduced clutter content provided by such pulse compressionsystem, improved subclutter visibility is provided and which is lessdependent upon system sighting angle. Accordingly, an alternatetechnique is employed.

One such alternate technique involves the use of a multiple-targettracker for determining the position difference between two proximatetargets detected during successive range trace intervals. In view of theamplitude and extent qualification employed in qualifying that targetdata which is subjected to range-rate discrimination, the probabletargets under surveillance need not represent an unduly large number.Therefore, the position difference between two successively observedtarget alarms may be indicative of the motion of a moving target ofinterest. Further, the change in target position occurring betweensuccessive observations or system pulse repetition intervals is, ofcourse, indica tive of the speed of such moving target. Thus, byemploying a nominal radial rate limit as a reference, a moving targetsuch as a submarine periscope may be distinguished from a bobbing oilcan. Further, by employing a maximum rate limit, such target may bedistinguished from other targets or phenomenon not of interest.

A block diagram of the general arrangement of such target qualificationis shown in FIG. 10, in which there is provided a two-limit amplitudecomparator 89, corresponding to elements 86, 87, and 88 of FIG. 9 and incooperation with time-averaged thresholding means and terminal 74, theoutput of comparator 89 being fed to a radial extent discriminator 90,corresponding to the arrangement of elements 80, 81, 82, 83 and 84 inFIG. 8. The amplitude and extent-qualified output of discriminator 90 isthen fed to a two-limit radial rate discriminator 91. Such latterelement may comprise a digitizer, digital memory bank and multipletarget tracker for performing range-rate discrimination of the amplitudeand extend-qualified target signal inputs thereto.

Other forms of processing of high resolution data may be employed. Forexample, where a discrete cultured target of interest displays a greaterdegree of reflectivity than the minimum clutter content of such highresolution data, it may be desired to distinguish a peak target returnfrom the background clutter for display by ordinary low-bandwidth,limited resolution

1. In a coded pulsed energy system, including an intermediate frequencyreceiver stage having a local oscillator input, time-domain correlationmeans comprising local oscillator injection means in cooperation withsaid intermediate frequency receiver for applying a coded periodicsampling signal at said local oscillator input of said intermediatefrequency receiver stage, the sampling periodicity of which samplingsignal is substantially less than the pulse repetition interval of saidsystem and the time-phase of which sampling periodicity is discretelyprogressively varied each pulse repetition interval by an amount lessthan said sampling periodicity, and the coding of which coded samplingsignal is a replica of that transmitted by said pulsed energy system;and data matrix storage means responsive to said variable time-phasesampled signals for reconstructing a range trace signal having animproved range resolution corresponding to the reciprocal of thetransmitted bandwidth.
 1. In a coded pulsed energy system, including anintermediate frequency receiver stage having a local oscillator input,timedomain correlation means comprising local oscillator injection meansin cooperation with said intermediate frequency receiver for applying acoded periodic sampling signal at said local oscillator input of saidintermediate frequency receiver stage, the sampling periodicity of whichsampling signal is substantially less than the pulse repetition intervalof said system and the time-phase of which sampling periodicity isdiscretely progressively varied each pulse repetition interval by anamount less than said sampling periodicity, and the coding of whichcoded sampling signal is a replica of that transmitted by said pulsedenergy system; and data matrix storage means responsive to said variabletime-phase sampled signals for reconstructing a range trace signalhaving an improved range resolution corresponding to the reciprocal ofthe transmitted bandwidth.
 2. The system of claim 1 in which said datamatrix means includes rangegated signal thresholding means and comprisesrange-gated time averaging means for determining and storing the averagesignal level of each pulse-compression range-bin of range trace signalssampled by said correlator of said system, and lower limit comparatormeans responsive to said range trace signals and to said average signallevels for providing a range-bin thresholded range trace signalindicative of a signal return at each range bin in excess of an averagesignal return at such range bin.
 3. The device of claim 2 in which thereis further included means responsive to said signal thresholding meansfor distinguishing targets having at least a minimum radial velocityrelative to said system and comprising means for comparing correspondingportions of successive range trace signal histories to determine thoseunlike corresponding portions indicative of the range-change of a targetoccurring during the interval between the occurrence of saidcorresponding portions.
 4. The device of claim 2 in which there isfurther provided spatial filtering means coupled to said signalthresholding means for distinguishing targets having at least apreselected minimum radial velocity relative to said system.
 5. Thedevice of claim 2 in which there is further included means fordistinguishing targets having at least a preselected minimum radialvelocity relative to said system and comprising first and second shiftregister means, each having an input responsively coupled to said signalthresholding means for providing a respective first and delayed secondrange trace signal histories; and nor-gate means having a first andsecond input respectively coupled to an output of a mutually exclusiveone of said shift register means, for providing an output indicative ofthe non-coincident states of compared portions of said first and delayedsecond time histories.
 6. The device of claim 2 in which said datamatrix means further includes upper limit comparator means responsive tosaid range trace signals and having a reference input responsivelycoupled to a biased output of said range-gated time averaging means, andlogic means responsely coupled to said upper and lower limit comparatormeans for providing an output indicative of a range-gated range tracesignal having an amplitude within preselected upper and lower amplitudelimits.
 7. The device of claim 1 in which there is a further providedspatial filter means responsive to said data matrix means for indicatingthe detection of a target having a radial extent within preselectedlimits.
 8. The device of claim 7 in whicH said spatial filter meanscomprises first logic means for determining the detection of a targethaving at least a preselected minimum radial extent; second logic meansfor determining the absence of a target having a preselected maximumradial extent, and third logic means responsive to said first and secondlogic means for providing an output signal indicative of the detectionof a target of at least said preselected minimum radial extent and lessthan said preselected maximum radial extent.
 9. The device of claim 1 inwhich said data matrix means comprises two-limit amplitude comparatormeans for indicating a target return signal for each range-bin andhaving an amplitude within preselected limits.
 10. The device of claim 1in which said data matrix means comprises two-limit amplitudecomparators means for indicating a target return signal from eachrange-bin and having an amplitude within a preselected upper amplitudelimit and above a selected threshold level associated with suchrange-bin; and in which there is further provided two-limit spatialfiltering means responsive to the output of said two-limit amplitudecomparator for indicating whether said amplitude-qualified signalrepresents a target having a radial extent within a preselected upperand lower radial limit.
 11. The device of claim 1 in which said codedpulsed energy system is of the pulse compression type and includes anintermediate frequency receiver stage having a receiver-mixer incooperation with a stable local oscillator for providing a source offrequency fs, and in which said local oscillator injection meanscomprises an intermediate frequency oscillator as a source of frequencyfIF; filtered mixing means responsive to the coded spectra (fT) utilizedby a transmitter of said pulse compression system and further responsiveto said sources of frequency fs and fIF for providing a local oscillatorinjection signal spectrum (fT -(fs + fIF)); and first receiver mixingmeans responsive to a pulse-compressed output of a receiver of saidpulse compression system and having a local oscillator input responsiveto said local oscillator injection signal for providing a lower sidebandfrequency translated output (fs + fIF) to an input of saidreceiver-mixer of said intermediate frequency receiver stage.
 12. Thedevice of claim 11 in which there is further provided radio-frequencyconditioning means in cooperation with said stable local oscillator forconverting received echoes of the radio frequency spectrum (fT)transmitted by said pulsed energy system to a conjugate side band of thetransmitted spectrum.
 13. The device of claim 11 in which there isfurther provided switchable dispersive delay means having a transmit andreceive switching modes, said delay means input-coupling a source ofsaid coded spectrum fT to a transmitter of said pulsed energy systemduring said transmit-switching mode to provide frequency modulation of apulsed transmission; and radio-frequency conditioning means incooperation with said stable local oscillator for converting receivedechoes of the transmitted radio frequency spectrum (fT) to a conjugatesideband of the transmitted spectrum, said delay means being interposedbetween an output of said radio frequency conditioning means and aninput of said first receiver mixing means during said receive switchingmode for providing a pulse compressed receiver input to said firstreceiver mixing means.
 14. In a pulse-compression type pulsed energysystem having a receiver, data processing means comprising two-limitamplitude comparator means responsively-coupled to said receiver forproviding an output indicative of a rangegated target return signal fromeach of successive range bins and having an amplitude within apreselected upper amplitude limit and above a selected threshold levelassociated with such range bin; and two-limit spatial filtering meansresponsive to the output of said two limit amplitude comparator forindicating whether said amplitude-qualified signal represents a targethaving a radial extent within a preselected upper and lower radiallimit.
 15. The device of claim 14 in which said two-limit spatial filtercomprises first radial extent signalling means responsive to saidtwo-limit amplitude comparator for providing an output indicative of thepresence of an amplitude-qualified target signal corresponding to atleast a preselected minimum target radial extent; second radial extentsignalling means responsive to said two-limit amplitude comparator forproviding an output indicative of the absence of an amplitude qualifiedtarget signal corresponding to at least a preselected maximum radialextent; and logic means responsive to said first and second radialextent signalling means for providing an output indicative of anamplitude qualified target signal representing a target having a radialextent within said two preselected radial extent limits.
 16. The deviceof claim 14 in which said two-limit spatial filter comprises an inputterminal; first and second coincident logic signalling means; firsttapped delay line means having an input coupled to said input terminaland further having a plurality of successive taps coupled to said firstcoincident logic signalling means, the interval between adjacent tapscorresponding to a sampled range bin and the plurality of tapscorresponding to a preselected minimum radial extent; second tappeddelay line means having an input coupled to said input terminal andfurther having a plurality of successive taps coupled to said secondlogic signalling means, the interval between adjacent taps correspondingto a sampled range bin and the plurality of taps corresponding to apreselected maximum radial extent; and third logic means responsive to afirst state of said first logic means and to a second state of saidsecond logic means for indicating an input signal on said input terminalhaving a duration corresponding to a radial extent greater than saidminimum radial extent and less than said maximum radial extent.
 17. Thedevice of claim 14 in which said two-limit spatial filter comprises aninput terminal; first and second coincident logic signalling means;tapped delay line means having an input terminal and further having afirst and second plurality of successive taps respectively coupled tosaid first and second coincident logic signalling means, the intervalbetween adjacent taps corresponding to a sampled range bin and the firstplurality of taps corresponding to a preselected minimum radial extent,said second plurality of successive taps including said first pluralityand corresponding to a preselected maximum radial extent; and thirdlogic means responsive to a first state of said first logic means and toa second state of said second logic means for indicating an input signalon said input terminal having a duration corresponding to a radialextent greater than said minimum radial extent and less than saidmaximum radial extent.
 18. In a frequency-modulation type pulsecompression system, narrow bandwidth intermediate frequency correlationmeans for processing wide bandwidth data without compromising the dataresolution limits thereof and comprising an intermediate frequencyreceiver stage including a mixer having a first input responsive toreceived echoes of frequency-modulated pulsed energy transmitted by saidsystem, and further having a second local oscillator input; aperiodically frequency-modulated local oscillator for providing duringeach system pulse repetition interval a pulse train offrequency-modulated pulses of like pulsewidth as said transmittedenergy, the frequency modulation of said pulse train differing from thatof said transmitted energy by an amount correspOnding to a preselectedintermediate frequency, said second input of said mixer being coupled toan output of said local oscillator; periodic programmer means forcyclically, discretely, progressively adjusting the time phase of saidlocal oscillator pulse train, relative to the occurrence of saidtransmitted energy, each system pulse repetition interval, saidprogrammer having a periodicity of n system pulse repetition intervals;and data matrix storage means responsive to said programmer and to saidintermediate frequency receiver stage for providing a range trace datamatrix of in range-gated data-elements corresponding to contiguous rangebins.
 19. In a frequency-modulation type pulse compression system,narrow bandwidth intermediate frequency correlation means for processingwideband width data without compromising the data resolution limitsthereof and comprising an intermediate frequency receiver stageincluding means providing a periodically frequency-modulated localoscillator input each pulse repetition interval, said local oscillatorinput comprising a pulse train of i frequency-modulated pulses of likepulsewidth as said transmitted energy, the frequency modulation of saidpulse train differing from that of said transmitted energy by an amountcorresponding to a preselected intermediate frequency, periodicprogrammer means for cyclically discretely, progressively adjusting thetime phase of said local oscillator pulse train, relative to theoccurrence of said transmitted energy, each pulse repetition interval,said programmer having a periodicity of n pulse repetition intervals;and data matrix storage means responsive to said programmer and to saidintermediate frequency receiver stage for providing a range race datamatrix of in range-gated data elements, corresponding to contiguousrange bins.
 20. In a pulsed energy system including afrequency-modulated transmitter and an intermediate frequency receiverstage responsive to received echoes of pulsed energy transmitted by saidtransmitter and having a local oscillator input, narrow bandwidthcorrelation means for processing wide bandwidth data withoutcompromising the data resolution limits thereof, and comprising localoscillator injection means cooperating with said intermediate frequencyreceiver stage for periodically sampling a received signal during eachpulse repetition interval to provide a range-bin sampled range tracesignal; and means for adjusting the time-phase of said periodic samplingfor increasing the number of range-bins sampled over a preselected dataprocessing interval.
 21. The device of claim 20 in which saidintermediate frequency receiver stage includes a plurality ofintermediate frequency receivers commonly responsive to said receivedechoes, each receiver having a separate local oscillator input; andwhich said local oscillator injection means comprises a like pluralityof local oscillators as intermediate frequency receivers, each localoscillator cooperating with a mutually exclusive one of said receiversfor sampling a mutually exclusive set of range-bins.
 22. The device ofclaim 20 in which there is further provided data matrix storage meansresponsive to said intermediate frequency receiver and said means foradjusting for reconstructing a range trace signal of improved resolutionfrom said range-bin signal samples.
 23. In a frequency modulated pulsedenergy system, including an intermediate frequency receiver stage havinga local oscillator input, time-domain correlation means comprising localoscillator injection means in cooperation with said intermediatefrequency receiver for applying a periodic sampling signal at said localoscillator input of said intermediate frequency receiver stage, thesampling periodicity of which sampling signal is an integer submultipleof the pulse repetition interval of said system and the time-phase ofwhich sampling periodicity is discretely progressively varied each pulserepetition intervaL by a submultiple of said sampling periodicity; anddata matrix storage means responsive to said variable time-phase sampledsignals for reconstructing a range trace signal having an improved rangeresolution corresponding to the reciprocal of the transmittedfrequency-modulation bandwidth, BW.
 24. A frequency modulated pulsecompression type pulsed energy system including an intermediatefrequency receiver stage having a receiver-mixer in cooperation with astable local oscillator for providing a source of frequency fs, andcomprising an intermediate frequency oscillator as a source of frequencyfIF; filtered mixing means responsive to the coding spectra (fT)utilized by a transmitter of said pulse compression system and furtherresponsive to said sources of frequency fs and fIF for providing a localoscillator injection signal spectrum (fT -(fs + fIF)); first receivermixing means responsive to a pulse-compressed output of a receiver ofsaid pulse compression system and having a local oscillator inputresponsive to said local oscillator injection signal for providing alower sideband frequency translated output (fs - fIF) to an input ofsaid receiver-mixer of said intermediate frequency receiver stage;switchable dispersive delay means having a transmit and receiveswitching modes, said delay means input-coupling a source of said codingspectrum fT to a transmitter of said pulsed energy system during saidtransmit-switching mode to provide frequency modulation of a pulsedtransmission; and radio-frequency conditioning means in cooperation withsaid stable local oscillator for converting received echoes of thetransmitted radio frequency spectrum (fT) to a conjugate sidebandthereof, said delay means being interposed between an output of saidradio frequency conditioning means and an input of said first receivermixing means during said receive switching mode for providing a pulsecompressed receiver input to said first receiver mixing means.
 25. In apulse compression type system providing a thresholded high-resolutionsignal output, means responsive to said signal output for providing afirst and a delayed second range trace signal, and means responsive tosaid first and said delayed second range trace signal for providing athird range trace signal indicative of detected moving targets.
 26. Thedevice of claim 25 in which the output of said second mentioned means isindicative of moving targets having velocities within a selected upperand lower velocity limit.